ICC judges find Thomas Lubanga was the president of the UPC/FPLC militia group Photograph: Evert-Jan Daniels/AFP/Getty Images

The international criminal court (ICC) issued its first judgment on Wednesday - a milestone in the path towards accountability.

In the judgment, the judges found that Thomas Lubanga was the president of the militia group known as the UPC/FPLC in the eastern region of the Democratic Republic of Congo during the non-international armed conflict from September 2002 to 14 August 2003.

The judgment makes several landmark findings. The charges concerned conscripting, enlisting and using children in armed conflict. The fact that the first ICC judgment concerns child soldiers shines a further spotlight on the need to protect vulnerable groups at risk during war.

The ICC built upon the jurisprudence from prior UN courts such as the special court for Sierra Leone in finding that the crime of child soldiers is committed as soon as the child joins the armed group - "with or without compulsion". This sets a high threshold prohibiting any use of children in fighting forces, even when families or children themselves may appear to support the child's involvement due to the coercive circumstances of armed conflict.

Similarly, the judgment established a high threshold for the protection of children was established concerning children who have an "indirect" role, such as children who may be forced to conduct domestic duties or general support activities which may not include taking up arms.

The judges found that, in such circumstances, the question is whether the child has been exposed to "real danger as a potential target." As a result, the judges found that both the "child's support and this level of consequential risk" meant that a child could be activity involved in hostilities even if she or he was absent from the immediate scene of the conflict.

The judges also paid particular attention to the experience of girl soldiers. The prosecutor had not specifically charged sexual violence and rape. During the trial, the appeals chamber rejected an attempt by the victims participating in the case to amend the charges to include gender crimes. However, in the course of presenting evidence, witnesses raised the use of girls in domestic work and the abuse of girls and women as sex slaves. This underscores the ever-prevalent risk of sexual violence during conflict and the need for vigilance in investigating all potential crimes, particularly crimes against women.

It is monumental that victims, including former child soldiers, where able to be involved directly in the trial. The ICC was the first such court to include victim participation in its statute. During the course of the trial, 129 victims participated through making submissions to the judges, by seeking to introduce evidence, and by questioning witnesses. Three victims themselves testified as witnesses.

Concerns were raised in the judgment regarding the prosecution's "lack of proper oversight" over their work with intermediaries. Intermediaries are non-court staff who may cooperate with the court in implementing various aspects of the court's work, and may potentially include people such as aid workers or local human rights monitors who are familiar with the local environment. They have assisted the ICC on a range of matters, including assisting victims to participate in proceedings, and judges in other cases at the ICC have been "mindful of the importance of their role".

It makes sense that an international court based outside the country under investigation - one covering all 120 countries who have accepted the court's jurisdiction and running 15 cases in seven countries - needs assistance from local people or organisations. Intermediaries facilitate activities such as locating or communicating with witnesses or victims particularly in settings without mobile phone coverage or transportation access.

In the judgment issued on Wednesday, however, the judges found that the prosecutor "should not have delegated its investigative responsibilities to the intermediaries as analysed in the judgment, notwithstanding the extensive security difficulties that it faced." The judges indicated that three prosecution intermediaries may themselves have committed a crime under the ICC Statute by potentially facilitating witnesses in giving false evidence. The evidence derived from interaction with these intermediaries was therefore excluded from consideration.

The court has learnt many lessons and last year compiled a draft set of guidelines on intermediaries. These draft guidelines are currently pending finalisation by the court and consideration by the countries who have accepted the ICC's jurisdiction, known as the state parties. The Open Society Justice Initiative strongly urges the court and the state parties to act upon the lessons learnt following the Lubanga judgment by adopting the guidelines on intermediaries at the assembly of state parties this November.

From here, the court now moves into the sentencing and reparations stages. After the judgment is translated into French for the defence, a separate sentencing hearing will take place. The judges have also requested submissions from the prosecution, defence and victims regarding how consideration of potential reparations ought to be conducted. This will be the first time the issue of reparations is addressed at the ICC.